Have I understood this solution to the sensor synchronization problem correctly?

by Sam Hammamy   Last Updated June 30, 2020 04:25 AM

I read a research paper which proposes an algorithm to synchronize sensors in a way that is independent of the sensors.

Beginning with the simplified version which assumes no drift between the sensor p and the host q clocks and assumes p does not send a time with its messages but consistently sends measurements at a rate of 75 Hz for example.

How do I obtain multiple measurements of p's and q's clock based on some starting event?

More specifically, let's say that p is an Ultrasonic Range Sensor, and q is a Raspberry-Pi running Linux.

Assuming p is a higher-end sensor with an ADC and can provide the distance values over SPI but without a timestamp; I realize that's not how these common sensors are but let's simplify things.

I also realize the SPI frequency of the Rpi is approx 3.5 kHz to 125 MHz, but let's again say we set the SPI clock such that we know p is generating measurements at 75 Hz.

Having these equations

enter image description here enter image description here enter image description here

where A is the constant offset between clocks, t is the time on the Rpi at which the sensor observed the data, and e is the latency by which the Rpi processes the message.

We cannot observe A or e directly but we know p and q.

If I say that q1 is the epoch time on the Rpi when I start the SPI communication to read one measurement, is the value of p1 simply

q1 + (1/75)

The author says this method is not useful and is illustrative of the basic idea of the approach, and having written it out like this does make that clear. But I want to verify I've understood it before moving on to the real algorithm.

Let's finally say I am using a common sensor that I have connected to an STM32 blue pill which the Rpi uses SPI to read the measurement, how does that change p1?

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